This invention relates generally to magnetic resonance imaging (MRI). Magnetic resonance imaging (MRI) is a non-destructive method for the analysis of materials and is an approach to medical imaging. It is generally non-invasive and does not involve ionizing radiation. In very general terms, nuclear magnetic moments are excited at specific spin precession frequencies that are proportional to the local magnetic field. The radio-frequency signals resulting from the precession of these spins are received using pickup coils. By manipulating the magnetic fields, an array of signals is provided representing different regions of the volume. These are combined to produce a volumetric image of the nuclear spin density of the body.
Magnetic resonance (MR) imaging is based on nuclear spins, which can be viewed as vectors in a three-dimensional space. During an MRI experiment, each nuclear spin responds to four different effects: precession about the main magnetic field, nutation about an axis perpendicular to the main field, and both transverse and longitudinal relaxation. In steady-state MRI experiments, a combination of these effects occurs periodically.
U.S. Pat. No. 4,843,322 to Glover, issued Jun. 27, 1989, which is incorporated by reference for all purposes, discloses a method for producing multi-slice MRI images. U.S. Pat. No. 7,928,729 to Hargreaves et al., issued Apr. 19, 2011, which is incorporated by reference for all purposes, discloses a distortion-free magnetic resonance imaging near metallic implants.